ELECTRORETINOGRAPHIC ALTERATIONS IN THE LAURENCE-MOON-BARDET-BIEDL PHENOTYPE

Maximal 0,5-Hz and cone 30-Hz ERG responses were recorded from 19 pati ents showing a Laurence-Moon-Bardet-Biedl (LMBB) phenotype. Off-line a veraging of 80 to 100 iterations was routinely performed, When needed, our previously described low-noise techniques and off-line fast Fouri er transform procedures were used, The maximal ERG response was non-de tectable in 52.6% of cases, About half of the recordable signals were below 5% of the lower normal amplitudes, Cone 30-Hz ERGs were measurab le in 64.7% of cases, Of these, 63% of tracings were below 5% of the l ower normal range. In most cases no dystrophic pattern was definable, due to severe reduction of both signals. Statistical analyses showed n o correlation between ERG amplitudes and residual visual field areas. Clinical and electroretinographic observations suggest that retinopath y in most LMBB patients is a widespread form of degeneration, initiall y affecting rods but rapidly involving cones as well, However, there a re also cases with a clear-cut cone-rod pattern, with fairly well pres erved maximal ERG responses. The lack of correlation between maximal E RG responses and visual field residual areas, different from non-syndr omic retinitis pigmentosa (RP) patients, could be related either to a low reliability of visual field testing in LMBB patients or to mechani sms accounting for the ongoing retinal degeneration in LMBB syndrome t hat are different from those of pure RP, Variable findings are in line ,vith the documented genetic heterogeneity of the syndrome.